Basic Watch Face

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android">

    <uses-feature android:name="android.hardware.type.watch" />

    <uses-permission android:name="android.permission.WAKE_LOCK" />
    <uses-permission android:name="com.google.android.permission.PROVIDE_BACKGROUND" />
    <uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED" />

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@android:style/Theme.DeviceDefault">

        <uses-library
            android:name="com.google.android.wearable"
            android:required="true" />

        <!--
               Set to true if your app is Standalone, that is, it does not require the handheld
               app to run.
        -->
        <meta-data
            android:name="com.google.android.wearable.standalone"
            android:value="true" />

        <activity
            android:name=".presentation.MainActivity"
            android:exported="true"
            android:taskAffinity=""
            android:theme="@style/MainActivityTheme.Starting">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <service
            android:name=".BarcodeWatchFaceService"
            android:directBootAware="true"
            android:label="@string/barcode_name"
            android:permission="android.permission.BIND_WALLPAPER"
            android:exported="true">
            <meta-data
                android:name="android.service.wallpaper"
                android:resource="@xml/watch_face" />
            <meta-data
                android:name="com.google.android.wearable.watchface.preview"
                android:resource="@drawable/preview_circular" />
            <meta-data
                android:name="com.google.android.wearable.watchface.preview_circular"
                android:resource="@drawable/preview_circular" />
            <intent-filter>
                <action android:name="android.service.wallpaper.WallpaperService" />
                <category
                    android:name=
                        "com.google.android.wearable.watchface.category.WATCH_FACE" />
            </intent-filter>
        </service>
    </application>

</manifest>

BarcideWatchFaceService.kt

package com.example.barcode

import android.util.Log
import android.view.SurfaceHolder
import androidx.wear.watchface.CanvasType
import androidx.wear.watchface.ComplicationSlotsManager
import androidx.wear.watchface.WatchFace
import androidx.wear.watchface.WatchFaceService
import androidx.wear.watchface.WatchFaceType
import androidx.wear.watchface.WatchState
import androidx.wear.watchface.style.CurrentUserStyleRepository
import androidx.wear.watchface.style.UserStyleSchema

class BarcodeWatchFaceService : WatchFaceService() {
    override fun createUserStyleSchema(): UserStyleSchema {
        return super.createUserStyleSchema()
    }

    override fun createComplicationSlotsManager(currentUserStyleRepository: CurrentUserStyleRepository): ComplicationSlotsManager {
        return super.createComplicationSlotsManager(currentUserStyleRepository)
    }

    override suspend fun createWatchFace(
        surfaceHolder: SurfaceHolder,
        watchState: WatchState,
        complicationSlotsManager: ComplicationSlotsManager,
        currentUserStyleRepository: CurrentUserStyleRepository
    ): WatchFace {
        Log.d(TAG, "createWatchFace()")

        val renderer = BarcodeCanvasRenderer(
            context = applicationContext,
            surfaceHolder = surfaceHolder,
            watchState = watchState,
            complicationSlotsManager = complicationSlotsManager,
            currentUserStyleRepository = currentUserStyleRepository,
            canvasType = CanvasType.HARDWARE
        );

        return WatchFace(
            watchFaceType = WatchFaceType.ANALOG,
            renderer = renderer
        );
    }

    companion object {
        const val TAG = "BarcodeWatchFaceService"
    }
}

BarcodeCanvasRender.kt

package com.example.barcode

import android.content.Context
import android.graphics.Bitmap
import android.graphics.Canvas
import android.graphics.Color
import android.graphics.Rect
import android.util.Log
import android.view.SurfaceHolder
import androidx.wear.watchface.ComplicationSlotsManager
import androidx.wear.watchface.Renderer
import androidx.wear.watchface.WatchState
import androidx.wear.watchface.style.CurrentUserStyleRepository
import com.google.zxing.BarcodeFormat
import com.google.zxing.qrcode.QRCodeWriter
import kotlinx.coroutines.CoroutineScope
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.SupervisorJob
import kotlinx.coroutines.cancel
import java.time.ZonedDateTime

private const val FRAME_PERIOD_MS_DEFAULT: Long = 16L

private const val BARCODE_TEXT: String = "Hello, World"

class BarcodeCanvasRenderer(
    private val context: Context,
    surfaceHolder: SurfaceHolder,
    watchState: WatchState,
    private val complicationSlotsManager: ComplicationSlotsManager,
    currentUserStyleRepository: CurrentUserStyleRepository,
    canvasType: Int
): Renderer.CanvasRenderer2<BarcodeCanvasRenderer.BarcodeSharedAssets>(
    surfaceHolder,
    currentUserStyleRepository,
    watchState,
    canvasType,
    FRAME_PERIOD_MS_DEFAULT,
    clearWithBackgroundTintBeforeRenderingHighlightLayer = false
) {
    class BarcodeSharedAssets : SharedAssets {
        override fun onDestroy() {
        }
    }

    private fun createQR(content: String, width: Int, height: Int): Bitmap {
        Log.d(TAG, "createQR()")
        val writer = QRCodeWriter()
        val bitMatrix = writer.encode(content, BarcodeFormat.QR_CODE, width, height)
        val bitmap = Bitmap.createBitmap(width, height, Bitmap.Config.RGB_565)
        for (x in 0 until width) {
            for (y in 0 until height) {
                bitmap.setPixel(x, y, if (bitMatrix.get(x,y)) Color.BLACK else Color.WHITE)
            }
        }
        return bitmap
    }

    private val scope: CoroutineScope =
        CoroutineScope(SupervisorJob() + Dispatchers.Main.immediate)

    override suspend fun createSharedAssets(): BarcodeSharedAssets {
        Log.d(TAG, "createSharedAssets()")
        return BarcodeSharedAssets()
    }

    override fun renderHighlightLayer(
        canvas: Canvas,
        bounds: Rect,
        zonedDateTime: ZonedDateTime,
        sharedAssets: BarcodeSharedAssets
    ) {
        Log.d(TAG, "renderHighlightLayer()")
        canvas.drawColor(Color.BLUE)
    }

    override fun onDestroy() {
        Log.d(TAG, "onDestroy()")
        scope.cancel("BarcodeCanvasRenderer scope clear() request")
        super.onDestroy()
    }

    override fun render(
        canvas: Canvas,
        bounds: Rect,
        zonedDateTime: ZonedDateTime,
        sharedAssets: BarcodeSharedAssets
    ) {
        //val qr_bitmap: Bitmap = createQR(BARCODE_TEXT, canvas.width, canvas.height)
        //canvas.drawBitmap(qr_bitmap, 0f, 0f, Paint())
        Log.d(TAG, "render()")
        canvas.drawColor(Color.RED)
        Log.d(TAG, "renderFinished")
    }

    companion object {
        private const val TAG = "BarcodeCanvasRenderer"
    }
}